1. Field of the Invention
The present invention relates to an integrable demodulator having a clock-controlled shift register for digital signals modulated onto carriers.
2. Description of the Prior Art
A digital demodulator is described, for example, in "Elektronik" 1975, Vol. 10, pp. 104-105, in which a decade counter with decoded outputs is loaded on its input side by means of the signal to be demodulated by way of parallel connection of a diode and an ohmic resistance, whereby a loading capacitance is provided between the signal input of the decade counter and ground. The outputs of the decade counter employed as a decoder feed the signal already demodulated in the diode-resistance-capacitance combination.
Such a demodulator circuit has the disadvantage of time-dependent charging and discharging curves, as well as a strong influence on the threshold values of a preamplifier given weak input signals. Moreover, it easily leads to distortions of the demodulated signal. In addition, it is extremely difficult to provide in monolithic semiconductor technology.
More specifically, such demodulators which are characterized by an externally pre-connected diode or, respectively, resistance and capacitance wiring, not only offer significant resistance against attempts for monolithic integration in MOS technology, but also lead to time-dependent discharging and charging curves which are conditioned by the capacitance provided at the input. As mentioned above, the discharge time constant leads to distortions of the demodulated signal. Also, a strong influence on the threshold values of the preamplifier given weak input signals as well as the danger of a mutilation of the code because of signal intrusions are considered as further disadvantages. Finally, a dimensioning of the resistance-capacitance combination at the input of the known demodulators represents a forced compromise between the integration time constant which should be large to prevent interference intrusions and the discharge time which should be small for small pulse distortions.